The present invention relates to measuring tools, and more specifically the present invention relates to a measuring tape which can be conveniently operated with one hand, and which has a mechanism to keep the blade be stretched when it is being delivered out for taking measurements.
A variety of measuring tapes have been disclosed, and have appeared on the market. These measuring tapes commonly use a spiral spring for automatic rewinding control. However, using a spiral spring to rewind the blade may cause the blade connecting end to be damaged or loosened easily, more particularly after a long use. Because the blade should be pulled out with the hand, the hand may be injured by the sharp edge of the blade during the operation. Further, these measuring tapes require two people to take a long measurement. It is not easy and may cause an error to,take a long measurement by one operator.
There is also known an electronic measuring tape which uses a magnetic reader to read measurements, and a motor-driven ratchet wheel mechanism to rewind the magnetic tape. This structure of electronic measuring tape is still not satisfactory in function because of the following disadvantages. 1. It is not practical for taking longer measurements by an operator without the assistance of another person. 2. The magnetic tape may be worn away gradually to effect its precision. 3. It is not suitable for taking measurements within the effect of a magnetic field. 4. The electronic circuit and component parts may be damaged easily by moisture. 5. The ratchet wheel may fail to work properly after long uses. 6. The teeth of the ratchet wheel may be damaged easily causing a transmission error. 7. The true-zero hook may be damaged or loosened easily because it strikes against the casing of the measuring tape each time the tape is taken up. 8. The user's hand may be injured by the tape as the tape is being taken up rapidly.
Further, either of the aforesaid measuring tape C, the tape blade C1 may be loosened or caused to deform easily, as it is been let off by the motor C2, as shown in FIG. 5. If the tape blade is loosely wound round the reel or deformed, it may get stuck half way up.